1. Field of the Invention
The present invention relates to an inspection apparatus for inspecting a funnel assembly of a cathode ray tube (CRT) and an inspection method therefor, and more particularly, to an inspection apparatus for inspecting a funnel assembly of a CRT which includes a glass funnel and a glass neck attached to the vertex of the funnel and an inspection method therefor.
2. Description of the Related Art
A CRT includes a glass panel on which images are formed, a conical glass funnel attached to the rear surface of the panel, and a tubular glass neck attached to the vertex of the funnel. An electron gun or guns for forming images are accommodated in the neck.
In the case that the axis of the neck is deviated or declined with respect to the axis of the funnel, an electron gun cannot be maintained in its proper place. In this case, a good quality of an image cannot be formed. Thus, after completion of sealing of the funnel with the neck, an inspection process of the funnel assembly is performed to measure a misalignment such as an eccentricity and a declination of the neck with respect to the funnel.
FIG. 1 is a front view showing a conventional inspection apparatus for inspecting a funnel assembly of a CRT. FIG. 2 is a partly enlarged front view for explaining an inspection method for inspecting a funnel assembly using the inspection apparatus of FIG. 1. As shown in these drawings, an inspection apparatus for inspecting a funnel assembly of a CRT (hereinafter, referred to as an inspection apparatus, simply) includes a frame 101 having a support platform 102 for supporting a funnel assembly 109 to be inspected, a stand 103 installed in the frame 101 and a detection unit 104 which is supported on the stand 103 for up and down movement. A manually-operated steering wheel 105 is provided on the stand 103, for up and down adjustment of the detection unit 104 to set an initial location. When a manipulating button is pressed after setting the initial location, a driving unit (not shown) raises or lowers the detection unit 104.
The funnel assembly 109 to be inspected is placed on the support platform 102 with the neck 113 directed upwards. On the lower skirt 115 of the funnel 114 are provided three pads 112 indicating reference points of the funnel 114. On the support platform 102 are provided three stoppers 110 positioned in correspondence to the pads 112, for setting an inspection location of the funnel assembly 109.
The detection unit 104 includes a cylindrical probe rod 106 extended downwards along the axis of the neck 113 and upper and lower probes 107 and 108 which can protrude on and retract from the external wall of the probe rod 106. The upper and lower probes 107 and 108 are disposed on the probe rod 106 each by three at equal angles. The probes 107 and 108 provide detected signals to a controller (not shown).
By the above structure, the funnel assembly 109 to be inspected is placed on the support platform 102, and the three reference pads 112 of the funnel 114 are fixedly maintained at the state contacting each stopper 110. Then, when the manipulating button is pressed, the probe rod 106 of the detection unit 104 is descended to be inserted into the neck 113. If the detection unit 104 falls down to a predetermined location, the upper and lower probes 107 and 108 on the probe rod 106 protrude until they contact the inner wall of the neck 113 and then retract again. A signal corresponding to a protruding distance of each probe 107 or 108 is supplied to the controller. The controller estimates the eccentricity and declination of the neck 113 based on the signals corresponding to the protruding distances. The signals supplied from the three probes disposed radially in the same plane are compared with one another, to estimate the eccentricity of the neck at a corresponding height. The signals between the upper and lower probes are compared with each other, to estimate the declination of the neck.
In the above conventional inspection apparatus, an inspection is performed at the state where the probe contacts the inner wall of the neck. Accordingly, in the case where the inner diameter of the neck is larger or smaller, a corresponding detection unit should be fabricated according to the inner diameter of the neck. That is, a respective dedicated detection unit should be provided with respect to a funnel assembly of a variety of sizes. Thus, it costs much to produce a detection unit and consumes much time and working hours to replace and maintain the detection unit. Also, as being the case, a support platform supporting the funnel assembly should be replaced together.
The above conventional inspection apparatus estimates a relative location of the neck with respect to a funnel fixed at a reference inspection location by the stoppers, in order to judge whether the neck bonding is good or not. Although it has been estimated that there is a defect on eccentricity or declination of the neck, the defect may be due to a drawback in a contour such as an incorrect setting of the funnel inspection location or a distortion of the funnel itself, not due to a sealing of the neck. The conventional inspection apparatus cannot correct the above errors and instead regards it as a deficiency of the neck bonding.